Inverted back plates build

grapplesaw

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Gepetto said:
Are you using the 0.009" thick Bergquist SIL-PAD 400 insulators Glen?

I have repaired several amps that were built using the green colored, very rubbery insulators. Those tended to pierce through without much coaxing. All the edges around the screw ends of the TO-3s had pierced the insulator in the shape of the transistor end.
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I could double them up for now to test. What do you think Joe?
 
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NavLinear said:
A double bagger?

Glen - I think your thingy is too long. The screws appear to be longer than 0.5". They may be poking something you don't want poked.
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I don't care what they size does matter!

I use two 1" screws as guides the put in the correct length one. Give lots of " wiggle room"
 
NavLinear

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grapplesaw said:
I don't care what they size does matter!

I use two 1" screws as guides the put in the correct length one. Give lots of " wiggle room"
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Ok - just checking. Is there any chance one of the screws in rows five or six on the problem channel are kissing the chassis? Maybe the final two rows pull down the backplane board enough to short one of the through hole leads. You may want to do this one screw at a time, loosely at first. This may help in finding the problem area.

I'll let Joe chime in when he is available, but looking at the data sheet for the Sil-Pads the dielectric breakdown voltage between the 0.007" and 0.009" pads is quite different.
 
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NavLinear said:
Ok - just checking. Is there any chance one of the screws in rows five or six on the problem channel are kissing the chassis? Maybe the final two rows pull down the backplane board enough to short one of the through hole leads. You may want to do this one screw at a time, loosely at first. This may help in finding the problem area.

I'll let Joe chime in when he is available, but looking at the data sheet for the Sil-Pads the dielectric breakdown voltage between the 0.007" and 0.009" pads is quite different.
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Dielectric Breakdown Voltage (Vac) .007 vs .009 3500, vs 4500
ASTM D149

The srews just stick trough no contact anywhere.

image.jpg


I mean see this


image.jpg image.jpg
 
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NavLinear

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That first photo took a while to figure out.

If the screws are free and clear, and the pads are new, maybe the screws are pulling the backplane down just enough... Thinking out loud here.
 
laatsch55

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So you've got it isolated to the left channel row 5. If you leave row 5 or and put in row six do you still have distortion?? Also , check for a sharp edge or burr on the affected row that could be trashing the sil-pads. Doubling of the sil pads is not recommended. Then you have too much squish. Are they grey or green??
 
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Correction---if you leave out row 5 and put in row 6 do you still have distortion?. Also, if you leave the 22196 in row 5 , but leave out the 21195 in row 5 do you still have distortion??
 
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laatsch55 said:
So you've got it isolated to the left channel row 5. If you leave row 5 or and put in row six do you still have distortion?? Also , check for a sharp edge or burr on the affected row that could be trashing the sil-pads. Doubling of the sil pads is not recommended. Then you have too much squish. Are they grey or green??
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Lee the distortion is from right channel when I populate either row 5 or 6
I just doubled up the SIL pad for that row, and just snugged the screws, the distortion came back!

I will wait for Joe's take on it but looking like I will replace the right backplate

It Looks like someone's pecker is in there messing things up

Ugh
 
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laatsch55 said:
Correction---if you leave out row 5 and put in row 6 do you still have distortion?. Also, if you leave the 22196 in row 5 , but leave out the 21195 in row 5 do you still have distortion??
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Yes to first part still have distortion when using 5 or 6 and only after screws are tighter but not when loose, I guess this completes the circuit

Have not tried only half a set but have swapped them with other units

I am not sure if tightening causes some minor short in back plate , seams unlikely, or if this is the straw that breaks the camels back and puts to much combined current through the system to cause some feadback or anomaly to distort the one half of the sine wave
 
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The outputs are paralleled so what we are doing is narrowing down the problem to two sockets on. the backplane.
 
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laatsch55

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I had a problem similar to this but not on a,White Oakes amp. IIRC it turned out to be an emitter resistor. But that was a long time ago....so I could be wrong. Running 2 - 21195s short won't hurt anything on a low power test...
 
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And I see from that one pic you are running an Ecuadorian tree frog, they are prone to parasitic oscillations, try subbing a Brazilian Web footed toad....
 
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laatsch55 said:
Leave the 21195s out of row 5 and 6 and see if the distortion is still there...
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Ok populate row 6 left channel all good

Populate row 5 &6 with 96 only all good
Add 95 in row 5 &6 loose still good
Tighten screws till they only contact driver 0 in lbs distortion

Conclusion something wrong after load increased with adding 94's to row 5 &6

Throws fresh pair 95's as well with same result

Still not sure what is up

Tomorrow I will pull row two three and tighten fife and six and see what happens

After that I guess I need to replace back plate
 
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Check for cold solder joints around those two sockets, if not that you could have some issues on the foil side of that backplane....
 
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laatsch55 said:
And I see from that one pic you are running an Ecuadorian tree frog, they are prone to parasitic oscillations, try subbing a Brazilian Web footed toad....
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How about this instead image.jpg

We took my great me few to aquarium for his birthday
Fun was had by all!
 
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I don't know....that may suffer from a common mode conduction problem...and the color has leached from its case....
 
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